DMC/2 ignition for 750 SF3 – where's the codeswitch?

[JulianE]

I want to improve the timing on my recently bought SF3 and am starting by checking the code for the ignition curve on the DMC/2 system. I'm getting bad-tempered vibration between 2500-3500 rpm.
The mystery is, I can't find the code switch to adjust the ignition curve.
See attached photos of the DMC box, which I've half removed from its mount behind the battery.
There isn't any "half-inch hole" that I can see (as described in the manual available on the forum) on the front or sides of the box. Is the hole underneath? Do I need to remove the box completely from the housing?
By the way, I'll check the TDC setting too – I just thought it would be easier to tweak the code first!
Many TIA,
Julian

 

[Schurminater]

hi Julian, I’m not familiar with the DMC for the 750’s however is it not on the underside of the box?….you will have to remove it from where it is mounted and there should be a rubber bung covering the hole to allow access to the curve adjustment.

 

[Schurminater]

It’s generally on the same side as the mounting studs

 

[Paul Marx]

I want to improve the timing on my recently bought SF3 and am starting by checking the code for the ignition curve on the DMC/2 system. I'm getting bad-tempered vibration between 2500-3500 rpm.
The mystery is, I can't find the code switch to adjust the ignition curve.
See attached photos of the DMC box, which I've half removed from its mount behind the battery.
There isn't any "half-inch hole" that I can see (as described in the manual available on the forum) on the front or sides of the box. Is the hole underneath? Do I need to remove the box completely from the housing?
By the way, I'll check the TDC setting too – I just thought it would be easier to tweak the code first!
Many TIA,
Julian

Start by checking the TDC marks of course, then check timing statically, then strobe it.
I doubt that the ignition is responsible for undue vibration.
Go over the usual, first carbs and then make sure that the engine is properly tight in the frame.

Paul

 

[JulianE]

You're absolutely right – on the underside, and as soon as I could be bothered to remove the battery, I could take everything out easily.
It's set on 1, so I'll try it on a flatter curve (9 or 10?) and see what magic it works. Thank you!

 

[JulianE]

Start by checking the TDC marks of course, then check timing statically, then strobe it.
I doubt that the ignition is responsible for undue vibration.
Go over the usual, first carbs and then make sure that the engine is properly tight in the frame.

Paul

Paul, your comments are interesting.
I mentioned the vibration to Richard Slater when I was talking to him about the bike's history a couple of weeks ago and he suggested correct TDC was vital where vibration was concerned on the twins. The carbs were balanced by Ged 500 miles ago, who said the engine was tight (but I'll check it again). Also see my reply to Schurminater.
Any views on the correct curve for a SF3? I've seen people mention 9 or 10 as the ones to choose.

 

[rez]

Here are the Curves 6 -10.

Rainer

 

[JulianE]

Here are the Curves 6 -10.

Rainer

Thank you Rainer, I'm guessing that it's trial and error for different SFs with different setups? I know the initial timing check needs to be done with curve 1.

 

[rez]

Julian,
Curve 1-5 are Curves with Ignition max 40deg. before TDC.
6-10 are Curves max. 37deg. before TDC =
much better.
My Experience, begin with Curve 6.

Rainer

 

[piranha-bro2]

Curve 6 looks pretty radical to my eyes. 30 deg adv at no more than 2500rpm and 37 deg at 3,000rpm! I'd be trying curve 10.

I run Ignitech on a modified SF and hit 30 deg at just under 4500rpm and max 35 at 5500rpm. I used the same curve on a std SF2 and it runs beautifully.

 

[JulianE]

What a wonderful place this forum is – to be sweating over a bike, in my case in my narrow ground-floor hall, and getting tech advice and a deep reservoir of experience as I go in real time.

I will now adjourn to reread you and decide on a first setting to try...

And report back when all is running. Multi-thanks to everyone!

 

[motoddrob]

Worth checking the timing marks using a piston stop or dial gauge.

 

[piranha-bro2]

Worth checking the timing marks using a piston stop or dial gauge.

Absolutely. And once you have a definitive TDC, a simple jig that bolts to the cases with a mark that is easier to align with the TDC mark on the freewheel make life easier.

 

[Paul Marx]

Paul, your comments are interesting.
I mentioned the vibration to Richard Slater when I was talking to him about the bike's history a couple of weeks ago and he suggested correct TDC was vital where vibration was concerned on the twins. The carbs were balanced by Ged 500 miles ago, who said the engine was tight (but I'll check it again). Also see my reply to Schurminater.
Any views on the correct curve for a SF3? I've seen people mention 9 or 10 as the ones to choose.

When we stopped by at Slaters on our way to the ILOC rally in Stirling in 2001, Richard Slater commented that he'd never seen so many 750s together. There were 5 of us.
Paul

Reckless Eric's bike: No brakes and about an inch of side play at the back of the swing arm.
A memorable trip.

 

[Paul Marx]

And if after all that, it still vibrates inordinately, either you're not used to vibration or your crank isn't at 360°
Paul